Identifying subsystems

The object level, as you see it now, lacks explicit structure and is essentially flat. For complex software systems, with many more nodes and arcs, the resulting visual clutter can be confusing. However, there is usually some organization.

Abstraction is one way of managing complexity. It is good software engineering practice to encapsulate a data type and its access functions into a software subsystem, forming an abstract data type.

The rigiedit program provides many ways to help you in identifying subsystems of related artifacts. These subsystems may, for example, represent high-level software components, personnel assignments, or other application-specific information.

To identify the data types in the system by filtering the Module nodes:

1. Choose Filter by Node Type ... from the Filter menu.

   A Filter by Node Type dialog appears for the active window.

   Filters are used to show or hide nodes and arcs of different types. This dialog presents a choice of node type filters each of which can be toggled on to hide or off to show the associated type of node.

   

2. Toggle on the Module item from the dialog.

   Click on the box beside Module.

3. Click Apply.

   Nodes representing functions are now filtered (hidden), making it easy to identify and select the data type nodes. (For simple examples, this isn't necessary.)

4. Move the Data nodes aside in the canvas.
5. Toggle off the Module item from the dialog and click Apply.

   Nodes representing functions are shown again.

6. Click Done to dismiss the dialog.

To identify the access functions of the list abstract data type:

1. Choose By Name ... from the Select menu.

   A Select by Name dialog appears. Selecting by name may be more useful for very large graphs.

2. Type list and click Select.

   The list Data node becomes selected.

   

3. Click Done to dismiss the dialog.
4. Click the Arc Type button in the Workbench window.

   An Arc Type palette appears.

   This palette causes certain selection operations to consider or match only specific arc types (data arcs, here). The any choice in the palette matches any arc type.

   

5. Pick the data item from the Arc Type palette.
6. Choose Incoming Nodes from the Select menu.

   All neighboring nodes along incoming arcs, that is, clients of list, are selected, identifying all functions that access the internal structure of the list data type (through a data arc).

   

To create a new subsystem node to represent the list abstract data type:

1. While holding down the shift key, left click the list node.

   The list Data node is added to the previously selected group of six Module nodes.

2. Choose Collapse from the Edit menu.

   A new subsystem node is created that has all of the previously selected nodes as its children, thus simplifying the graph in the active window. The previously selected nodes are moved to a lower level in the hierarchy (and are deselected). The new node is of type Collapse and becomes selected. Composite arcs are added to relate the new node to other nodes in the window.

   

   Tip: To undo a collapse, choose Expand from the Edit menu for the subsystem node.

3. Right-click on the new subsystem node.

   A Node menu appears. You can bring up a Node menu on any node, even if it is not selected; the available choices apply to that node. Canvas menus in rigiedit are context sensitive and depend on what node or arc is under the pointer.

4. Choose Rename from the Node menu, type ListADT, and press the enter key.

   

   The new subsystem node is renamed to ListADT.

5. Activate the Overview window.

   Tip: [2.25in] Right-clicking on the canvas of the window to activate it does not disturb the current selection.

6. Choose Update from the Window menu.

   The hierarchy in the Overview window is updated to reflect the newly created subsystem.

   

On your own, return to the Children window and identify the four Module clients of the element Data node. Note that the element data type has a recursive data dependency and is a client of itself. Collapse the five selected nodes to form another subsystem node called ElementADT.

Collapse the remaining two nodes into another subsystem and name it Control. Update the Overview window and move aside the Children window so that you can find it more easily for operations in the rest of the tutorial.